Restoring Nextcloud after web server reinstallation

Hi folks,

I ran into some serious network and apache2 issues so I had to reinstall the whole LAMP configuration. Luckily, I am saving my nextcloud data on an external hard drive and had an old database backup (which sadly was not the newest one (Feb 28, 2018…) so might hold a different version of some modules than my webspace’s backup has saved) on it and had my old /var/www/html folder saved so I reinstalled LAMP as explained in the official nextcloud example configuration (click this! and downwards from there).
Later, copied the old html folder to /var/www/html and imported the mysql dump file via mysql -u blah -p foobar nextcloud < dump.bak.

The server’s running just fine again but trying to access the nextcloud only shows me:

`Internal Server Error

The server encountered an internal error and was unable to complete your request.
Please contact the server administrator if this error reappears multiple times, please include the technical details below in your report.
More details can be found in the server log.`

Is there anything I missed there? I really need that cloud to get back running asap b/c there’s some very sensible stuff on it some people need (yes I know I’m stupid af because I don’t do regular SD card backups or use RAID or whatever, it’s my first try, forgive me my inexcusable failure) so I would really appreciate all kinds of hints you can give me.

Thanks a lot in advance! Cheers, taiBsu